A railway vehicle is usually provided with a brake which automatically closes if the electric power to the vehicle is cut off or fails. Thus the electric motor of such a brake normally serves not to drive the brakeshoe or shoes against the braking member of the vehicle, but instead serves to pull such brakeshoes away from the braking element, with a spring or pack of springs normally wedging the brakeshoes into engagement with the brake element, normally a disk.
With such a brake the drive motor is usually an electric motor having a rotary motor output connected to a travelling-ball transmission whose output member is connected on one side to the operation member of a spring pack and on its other side is connected to a lever arrangement that operates in turn on a coupling element displaceable transversely to the longitudinal axis of the rotary drive. This coupling element is connected to one arm of a caliper which is linked to the other caliper arm so that when displaced in one direction the two caliper arms will grip the brake disk and slow or stop the vehicle.
Such an arrangement can be used both as the service brake of a railway vehicle or as an emergency brake. This type of electrically resettable brake is normally relatively bulky and quite complex. It requires frequent servicing and often responds relatively slowly, particularly after some wear.